Wave transmission network



Oct. 23, 1934. o. J. ZOBEL 1,277,751

WAVE TRANSMISSION NETWORK Filed March 18, 1933 INVENTO? 0. J. ZOBELPatented Oct. 23, 1934 1,977,751 WAVE TRANSMISSION NETWORK Otto JuliusZobel, New York, N. Y., assignor to American Telephone and TelegraphCompany, a corporation of New York Application March 18, 1933, SerialNo. 661,593

12 Claims. (01. 118-44) This invention relates to wave transmissionnetworks and more particularly to reactance networks, such as broad bandwave filters, of the unbalanced type in which one side of the circuitmay be grounded.

An object of the invention is to provide a new and improved type of wavetransmission network which is equivalent in its transmissioncharacteristics to known types of networks, but the component reactancesof which fall within a different range of values. Anotherobject is topermit the construction of transmission networks of the bridged-T typewhich otherwise would require the use of reactance elements which aretoo large or too small to be builtcommercially.

A further object of the invention is to reduce the cost of manufacturingwave filters, especially those of the unbalanced type.

The, bridged-T type of network is commonly employed in unbalancedcircuits since, for such circuits, it provides a network having the samedegree of generality in transmission characteristics as is given by thelattice network for balanced systems. In'one form, the bridged-T networkcomprises a bridging branch and a central branch, connected by means ofa unity ratio transformer the'two windings of which are connected seriesaiding and have substantially perfect coupling. In certain instances,however, the component reactance elements required to build the bridgingbranch used in this type of network may involve inductance coils whichare too large for economical manufacture, or condensers which are toosmall to permit the required precision of adjustment. In accordance withthe present invention these di iiiculties are obviated by resort- 1branch fall within an entirely different range of values than theyotherwise would. The inductance coils'may then be manufactured moreeconomically and the condensers may be adjusted with the requiredprecision. This desirable result is accomplished by shunting all or apart of the bridging impedance across one only of the windings of thecoupling transformer.- The transmission and impedance characteristics ofthe network are left undisturbed b l his modifica ion; 7 I

The nature of the invention will be more fully understood from thefollowing detailed description and by reference to the accompanyingdrawing, of which Figures 1 and 2 show schematically a transmissionnetwork of the bridged-T type, to which the inventionis applicableyand IFigs. 3, 4, 5 and 6 illustrate various embodiments of the invention.

' The transmission network shown schematically in Fig. 1 is of the wellknown bridged-T type.

It comprises a transformer having two equal windings L, L connectedseries aiding with mutual inductance M equalsubstantially to L, abridging impedance Z1 connected between the outer terminals 10, 12 ofthe transformer, and a shunt impedance Z2 connectedfrom the commonterminal 11 of the two inductances-L, L to the other side of the line,which may be grounded or otherwise fixed in potential. The impedances Z1and Z2 may comprise reactances only, or both resistance and reactanceelements, and generally they will have dilferent impedancecharacteristics. The network has the same degree of generality inrespect to its transmission and impedance characteristics as can beobtained with any fourterminal transmission network made up wholly ofpassive impedance, and it may be made either 5 balanced or unbalanced inform. For a more detailed description, explaining how the network may bedesignedto'have any desired transmission characteristics, reference ismade to the patent to H. W. Bode,,No. 1,828,454, issued October '90 20,1931. Y a

In certain instances it has been found that the network shown in Fig. 1may be built more economically if the impedance required for the branchZ1 is reduced in magnitude. For example; the inductances may be so largethat they cannot be conveniently wound on a single core, or thecapacitances may beso small that it is .impossible to obtain thenecessary precision of adjustment. Inaccordance with the inventiontheserestric- 10o tions areremoved by resorting to a new type of networksection in which apart or all of the impedance 'Z1.is shunted acrossoneonlyof the transformer windings L. Inone embodiment of the invention,shown schematicallyin Fig. 3;the bridging impedance Z1 isreplaced by twoimpedanceseach equal to A2 Z1, one being shunted across each of thewindings L. The inductances form- .ing the impedance /2 Z1 will, ofcourse, be only one-half the magnitude of those required for the 1110 bya factor of four, as compared with the corre sponding elements requiredin the impedance Z1.

In this way the elements required for the bridging branch are made tofall within an entirely different range of values, permitting theconvenient building of the inductance coils and allowing the requisiteclose adjustment of the condensers.

In a modification of the invention only a part of the bridging impedanceis relocated. In Fig. 2 the impedance Z1 has been replaced by thethreebranches Za, Zb and Zc, the parallel impedance of which is equal to Z1.1 In equation form,

1 l 1 1 zfz. Z1, 2.

As shown in Fig. 5, the portion of the bridging impedance represented bythe impedance Zb may be replaced by an impedance in magnitude equal toA1 Zb shunted across only one of the windings L, between the terminals11, 12. Likewise, the part of Z1 represented by Zc may be replaced bythe impedance Zc shunting one of the transformer windings L, betweenterminals 10, 11. The two impedances Zb and V Zc may, if desired, beconnected across the same winding L, for example, between the terminals10, 11. In this way the portion of the bridging impedance Z1 havingelements which are satisfactory in size is left undisturbed, whereas theother parts of Z1 are altered in magnitude by a factor of four andconnected in parallel with only one of the transformer windings L. Asshown in Fig. 6 the impedance A1 Zb of Fig. 5 may be replaced by twoimpedances each equal to /2 Zb, one being-shunted across each of thewindings L. Other combinations and permutations involving the impedancesZa, Zb and Z0, which may be advantageously employed under certaincircumstances, will readily suggest themselves. However, the networksillustrated by Figs. 5 and 6 are representative.

In the arrangements shown in Figs. 3, 5 and 6 if the impedancesconnected in parallel with the transformer windings comprise a shuntingvcapacitance its value may be decreased to compensate individually forthe inevitable interwinding capacitances of the two windings, L, Lofthe-transformer, effective, respectively, between the terminals 10, 11and between the terminals 11, 12. When this is done an improvement iseffected in the transmission and impedance characteristics of thenetworks. I

As mentioned above, the networks of the invention may be employed whereany other four-terminal transducer, comprising only passive impedances,may be used. The invention is applicable, for example, to'wave filters,phase correctors, delay networks and other transmission networks.

What is claimed is:

. 1. A wave transmission network comprising a pair of equal inductances,inductively coupled, in series with one side of the line, saidinductances being connected in series aiding relation, two impedances,one shunted across each of said inductances, and a third impedanceconnected from the junction of said inductances to the other side of theline.

2. A wave transmission network comprising in one side of the line a pairof equal inductances connected series aiding with unity coupling factor,a pair of equal impedances, one of said impedances being connected inparallel with each of said inductances, and a third impedance connectedbetween the common terminal of said pair of inductances and the otherside of the line. Y 3. A wave transmission network having a pair ofinput terminals and a pair of output terminals, said network comprisingan electrical path between each input terminal and a correspondingoutput terminal, in one of said paths a transformer having, two equalwindings connected series aiding with unity coupling factor, two generalimpedances, one of said impedances shunting each of said transformerwindings, and a third general impedance connected between the junctionpoint of said transformer windings and a point in the other of saidpaths.

4. A wave transmission network having a pair of input terminals and apair of output terminals, said network comprising an electrical pathbetween each input terminal and a corresponding output terminal, a pairof equal inductances connected series aiding with unity coupling factorin one of said paths, a pair of equal impedances, one of said impedancesshunting each of said inductances, and a third impedance included in ashunt path between the junction point of said inductances and a point inthe other of said paths.

5. A wave transmission network comprising a pair of input terminals anda pair of output terminals, said network comprising an electrical pathbetween each input terminal and a corresponding output terminal, a pairof equal inductances connected series aiding with unity coupling factorin one of said paths, a pair of equal reactances, one of said reactancesshunting each of said inductances, and a third reactance connectedbetween the junction point of said inductances and a point in the otherof said paths.

' 6. A wave transmission network comprising a pair of input terminalsand a pair of output terminals, said network comprising an electricalpath between each input terminal and a corresponding output terminal, apair of equal inductances connected series aiding with unity cou plingfactor in one of said paths, a general impedance connected in parallelwith one of said inductances, and a second general impedance connectedbetween the junction point of said inductances and a point in the otherof said paths.

7,. A wave transmission network comprising a pair of input terminals anda pair of output terminals, said network comprising an electrical pathbetween each input terminal and a corresponding output terminal, a pairof equal inductances connected series aiding with unity coupling factorin one of said paths, a general impedance connected in parallel withsaid inductances between the outer terminals thereof, a pair of equalinpedances, one of said pair of impedances being connected in parallelwith each of said inductanceS and a fourth general impedance connect-.ed between the junction point of said inductances and a point in theother of said paths.

' 8. A wave transmission network comprising a pair of input terminalsand a pair of output terminals, said network comprising an electricalpath between; each input terminal and a corresponding output terminal, apair of equal inductances I pedance shunting one of said inductances, athird general impedance shunting the other of said inductances, and afourth general impedance connected between the junction point of saidinductances and a point in the other of said paths.

9. A wave transmission network in the form of a T-network, the seriesarms of the T-network comprising a pair of equal inductances connectedin series aiding relation with mutual inductance therebetween, a generalimpedance shunting one of said inductances, and a second generalimpedance shunting the other of said inductances, and the shunt arm ofthe T-network comprising a third general impedance.

10. A wave transmission network in the form of a T-network, the seriesarms of the T-network comprising a pair of equal inductances connectedin series aiding relation with mutual inductance therebetweensubstantially equal in magnitude to the self-inductance of one of saidequal inductances, and a general impedance shunted across one of saidinductances, and the shunt arm of the T-network comprising a secondgeneral impedance having a characteristic differing from that of saidfirst-mentioned general impedance.

11. A wave transmission network of the ladder type comprising a pair ofequal impedances connected in series in one side of the line and a thirdimpedance in shunt with the line, connected between the common terminalof said pair of equal series impedances and the other side of the line,said equal series impedances comprising two equal inductances connectedin series aiding relation with unity coupling factor, and a pair ofequal impedances, one shunting each of said inductances.

12. An electric wave filter comprising a pair of equal inductancesconnected series aiding with unity coupling factor, a reactive impedanceshunting one of said inductances, a second reactive impedance shuntingthe other of said inductances, and a third reactive impedance having oneof its terminals connected to the junction point of said pair of equalinductances.

O'I'IO J. ZOBEL.

